1. Field of the Invention
Furan is hydrogenated in an aqueous system in the presence of a nickel catalyst and a dicarboxylic acid having 4 to 10 carbons to produce 1,4-butanediol and tetrahydrofuran.
2. Prior Art
Furan has been hydrogenated in a neutral or weakly acid aqueous system in the presence of a nickel catalyst as shown by Russian Pat. No. 114,928 (1958) to P. A. Moshkin et al. to produce 1,4-butanediol, tetrahydrofuran and small amounts of butanol. One example shows the inclusion of a small amount of formic acid in the reaction mixture. James A. Watson, Ind. Eng. Chem. Prod. Res. Develop. 12 (4) 310-311 (1973) shows the same general reaction where acetic acid is present in the reaction mixture. In both processes the yield of 1,4-butanediol is not as high as could be desired and unwanted by-products are produced, such as the mono- and diformate, and mono- and diacetate esters of 1,4-butanediol. These esters have boiling points quite close to the boiling point of 1,4-butanediol itself and it is expensive and difficult to distill them off; in fact the diacetate ester of 1,4-butanediol has the same boiling point as 1,4-butanediol and cannot be separated by distillation. Accordingly the 1,4-butanediol produced by these processes contains the said esters as impurities. Pure, "polymer grade" 1,4-butanediol is necessary in the manufacture of useful high molecular weight polyesters from terephthalic acid, for example, and accordingly the impure diol produced by the above-mentioned prior art processes cannot be used directly. The present invention yields polymer grade 1,4-butanediol directly by the simple expedient of avoiding the formation of the undesired esters.